We recently got this from the pediatrician at DS5's preK screen:

Doc: "Do you have any concerns about learning letters or anything?"
Me: "No, he reads at a pretty high level."
Doc: "Oh, so you've been teaching him to read?"
Me: "No, he taught himself to read somehow."

The doc got it then, and said he was almost embarrassed then to offer the book they hand out to all pre-k-ers. I assured him that DS likes all variety of books still, but we didn't get the book. frown

We did have flash cards when DS was little, but I got them because the pictures were cute and DS was so into signs and letters I knew he'd like them. And he did. But we didn't ever quiz him or anything.